Vehicle generator control

ABSTRACT

Control apparatus for maintaining constant speed of an AC generator carried aboard a motor vehicle having an engine, a transmission including a power take-off, and an AC generator. The control apparatus includes a hydraulic pump driven from the power take-off, a hydraulic motor drivably connected to the generator, a fluid circuit driving the hydraulic motor from the hydraulic pump, a closed center proportional servo control valve assembly controlling the fluid circuit, and a control circuit disposed to control the proportional control valve assembly. The control circuit includes an eddy current detecting speed sensor disposed to sense rotational speed of the hydraulic motor, or alternatively, includes an AC generator frequency reference signal generator, a comparing subcircuit which compares sensed speed of the hydraulic motor to a reference signal provided by a digital variable pulse generator, manual controls, an automatic ramp generator which controls acceleration of the generator such that acceleration proceeds gradually from a stopped condition to full operating speed, an annunciating display, and a main circuit breaker. The control valve assembly throttles both pressurized fluid entering the valve assembly from the pump and also spent fluid being returned to the pump through the valve assembly, thereby equalizing pressure drop on each side of the valve assembly. The hydraulic system includes a fluid storage tank, an oil filter, and an oil cooler.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to control of vehicle mounted, enginedriven generators for the purpose of stabilizing frequency and voltagecharacteristics of generator output. The invention finds applications invehicles equipped with electrically operated auxiliary apparatusdependent upon stable alternating current (AC) electrical power, whereinground vehicles, boats, and aircraft are provided with generators drivenby the prime power-plant of the vehicle. Examples of vehicles whichcould benefit from incorporating the invention include rescue andmilitary vehicles having AC powered communications equipment, utilityand telephone company repair and maintenance vehicles, vehiclesproviding electrical welding equipment, and other vehicles utilizing ACequipment powered directly from an engine driven AC generator.

2. Description of the Prior Art

Many vehicles carry aboard equipment which is electrically operated byalternating current. Ordinary vehicular generators-are typicallydesigned to convert AC output to DC for the purpose of charging thebattery, and for supplying originally installed vehicular electricalequipment which is DC operated for compatibility with a battery basedvehicle electrical system. As functions of vehicles have been increasedover the years, it has become possible to drive an auxiliary generatorfrom the engine or principal power plant of the vehicle. Typically thisis accomplished by connecting the generator to a power take off or toany other suitable point of connection to engine output. While this willindeed operate a generator, variations in engine speed will wreak havocwith characteristics of power output and therefore with equipment whichis dependent upon stable voltage and frequency characteristics ofelectrical power.

U.S. Pat. No. 4,287,429, issued to Oleg I. Bashnin et al. on Sep. 1,1981, sets forth a control circuit for controlling the output of ahydraulically driven generator. The hydraulic circuit of Bashnin isappropriate for a large scale hydroelectric generator, but lacksstructure appropriate for a motor vehicle mounted generator, as seen inthe present invention. Notably, a small hydraulic motor, oil filter, oiltank, oil cooler, and small hydraulic controls are not shown in Bashnin.

U.S. Pat. No. 5,028,221, issued to Jean Malfit on Jul. 2, 1991, setsforth an improved generator receiver which is a mechanical componentdisposed in the power train of a generator. This mechanical componentlacks a control scheme including a comparison circuit and a master spoolvalve for assuring that the driven element rotate at constant speed, asseen in the present invention.

U.S. Pat. No. 5,421,705, issued to Hartmut, Benckert on Jun. 6, 1995,describes a safety limit control for a concrete pump. The control limitsthe amount of concrete being pumped to avoid stalling of a diesel powerplant. The system of Benckert does not vary hydraulic output of a pumpsuch that the output to an associated hydraulic motor is constantdespite fluctuating input speeds from the motor. The control scheme ofBenckert lacks the comparison circuit and hydraulic circuit of thepresent invention.

U.S. Pat. No. 3,941,016, issued to Gerhard Will on Mar. 2, 1976,describes a hydraulic pressure generator which produces pressureresponsive to engine speed. Logic of operation is opposite that of thepresent invention. Will provides a variable output for the purpose ofassisting in determining when to cause an automatic transmission tochange gears. The present invention provides a constant outputregardless of input speed from the engine so that the element driven bythe engine rotates at a constant speed.

U.S. Pat. No. 5,410,943, issued to Gilbert Kervagoret on May 2, 1995,sets forth a progressively opening control valve for a motor vehicleanti-skid braking system. This valve lacks the control system as seen inthe present invention, which control system includes a comparisoncircuit utilizing a rotational speed sensor and a reference source. Thevalve of Kervagoret is a single component of a hydraulic circuit, ratherthan comprising a complete circuit as seen in the present invention.

The need for controlling speed of an AC generator mounted in a motorvehicle, wherein the principal engine of the vehicle also drives thegenerator, has not been answered in the prior art. None of the aboveinventions and patents, taken either singly or in combination, is seento describe the instant invention as claimed.

SUMMARY OF THE INVENTION

The present invention provides a control scheme for assuring that agenerator carried aboard a motor vehicle and driven by the principalpower plant of the motor vehicle be driven at constant speeds. This isan important condition for assuring proper operation of AC operatedequipment carried aboard the vehicle. In vehicles wherein an ACgenerator is powered by the engine of the vehicle, variations in enginespeed threaten to disrupt operation of equipment dependent upon stablevoltage and frequency characteristics of the electrical power. Sinceengine speeds vary with demand for power to propel the vehicle, thenovel control scheme provides a hydraulic system which operates thegenerator at constant speeds despite variations in engine speeds.

This is accomplished by providing a hydraulic pump coupled to the outputof the engine of the vehicle, and driving a hydraulic motor therefrom.The generator is driven by the hydraulic motor. A control valve assemblyis interposed between the hydraulic pump and the hydraulic motor toapportion pressurized hydraulic fluid from the pump such that thehydraulic motor receives a constant flow rate. A control circuit sensesoperating conditions and controls the control valve assemblyappropriately to maintain the constant flow rate.

Auxiliary functions of the system include providing gradual accelerationof the generator when starting from the stopped condition, adjustment ofgenerator output characteristics, and cooling of hydraulic fluid.Gradual acceleration or “soft start” mitigates or eliminates damagewhich might otherwise result from abrupt connection to engine power. Theperiod of acceleration from the stopped condition to full speed isadjustable within a range of ten seconds to one minute, and may becontrolled by a human operator of the system. Combined with protectionfrom fluid overheating, the motor, seals, fluid conduits, and controlvalves are protected from damage associated with viscous fluid.

A particularly advantageous feature of the invention is that the controlvalve assembly meters fluid flow in both inlet and outlet directions,thereby maintaining pressure drop on both sides of the control valveassembly almost equal. This increases efficiency by reducing heat andpower losses, and assists in virtually eliminating overspeed andunderspeed of the generator as conditions change.

The apparatus is self-contained and readily retrofit to a motor vehiclehaving a power take-off. The apparatus includes a circuit breaker sothat, combined with ability to manage generator speed and to limit fluidtemperatures, the apparatus is self-protecting. A display annunciatesoutput voltage, output frequency, output amperage, generator rotationalspeed, and elapsed time of operation.

Accordingly, it is one object of the invention to provide control of agenerator driven by the engine of a motor vehicle such that generatorspeed and hence electrical output remain constant despite fluctuationsin engine speed.

It is another object of the invention that the control system virtuallyeliminate overspeed and underspeed as the system adjusts fluid input tothe hydraulic motor driving the generator responsive to fluctuations inspeed of the engine of he motor vehicle.

It is a further object of the invention that the apparatus beself-protecting from damage to overpressure and overtemperature ofpressurized hydraulic fluid.

Still another object of the invention is to provide annunciation ofgenerator output characteristics.

An additional object of the invention is that the apparatus beself-contained and readily retrofit to motor vehicles having powertake-offs.

It is still a further object of the invention that acceleration of thegenerator from the stopped condition be gradual.

Yet another object of the invention is to provide selectively variabletime of acceleration of the generator from the stopped condition to fulloperating speeds, and to enable a human operator to select the rate ofacceleration.

It is an object of the invention to provide improved elements andarrangements thereof in an apparatus for the purposes described which isinexpensive, dependable and fully effective in accomplishing itsintended purposes.

These and other objects of the present invention will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features, and attendant advantages of the presentinvention will become more fully appreciated as the same becomes betterunderstood when considered in conjunction with the accompanyingdrawings, in which like reference characters designate the same orsimilar parts throughout the several views, and wherein:

FIG. 1 is a diagrammatic, top plan view of a motor vehicle embodying thepresent invention.

FIG. 2 is a schematic diagram of the hydraulic circuit of the embodimentof FIG. 1.

FIG. 3 is a diagrammatic detail view of part of the hydraulic circuit ofFIG. 2, showing details of the proportional control valve assembly.

FIG. 4 is a schematic diagram of electrically and electronicallyoperated components of the motor vehicle of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 of the drawing shows a motor vehicle 10 having a chassis 12, anengine 14, a transmission 16, and wheels 18, 20, 22, 24 suspended fromchassis 12. Engine 14 provides torque to transmission 16, which in turndrives wheels 22, 24 through a suitable drivetrain including adriveshaft 26, differential assembly 28, and a rear axle 30. Theaforementioned components of vehicle 10 are conventional and need not bedescribed further herein apart from noting that chassis 12 is intendedin a representative sense. That is, objects described as being supportedon chassis 12 may be indirectly supported. For example, an object may befixed to the body (not separately shown) or to any other structurallysturdy component of vehicle 10 which is ultimately fixed to chassis 12.Transmission 16 has a power take-off 32 for driving diverse rotatableequipment (not shown).

Motor vehicle 10 is improved according to the present invention byproviding an alternating current (AC) generator 34 carried aboardvehicle 10. Generator 34 is driven at a constant speed despitefluctuations in speed of engine 14 by an automatically controlledhydraulic system. The constant speed may be any selected speed, but willusually be that assuring that frequency of generator output be 60 Hz, sothat sensitive equipment (not shown) carried on vehicle 10 will operateproperly. Illustratively, for a two pole, single phase generator, apreferred constant speed is 3,600 revolutions per minute (RPM).

Principal hydraulic components of the embodiment of FIG. 1 include ahydraulic pump 36 connected to and driven by power take-off 32, ahydraulic motor 38 (see FIG. 2), and a proportional control valveassembly 40 (see FIG. 2). Turning to FIG. 2, pump 36 is a conventionalpump having an inlet (not separately shown) disposed to receive fluidfor pumping and an outlet (not separately shown) for discharging pumpedfluid under pressure. Hydraulic motor 38 is drivably connectable togenerator 34 by a shaft 42. Motor 38 may be a conventional hydraulicmotor having an inlet (not separately shown) disposed to receive fluidunder pressure and an outlet (not separately shown) disposed todischarge spent fluid for recirculation to pump 36.

The fluid circuit depicted in FIG. 2 includes a supply conduit (shown tocomprise two sections 44A, 44B) disposed to conduct pressurized fluiddischarged by pump 36 to motor 38, and two recirculating conduitsdisposed to return fluid discharged by motor 38 to pump 36. The firstrecirculating conduit 48 is disposed to return fluid discharged by pump36 directly back to the inlet of pump 36, bypassing motor 38. The secondreturn conduit includes sections 46A, 46B, 46C, 46D, 46E. A fluid filter50, a hydraulic fluid cooler 52, and a hydraulic fluid storage tank 54are disposed serially with respect to the second return conduit. Abypass conduit 56 is arranged to enable returned fluid to bypass storagetank 54. Hydraulic fluid cooler 52 comprises a heat exchanger (notseparately shown) disposed to dissipate heat to ambient air, anelectrically operated fan 53 disposed to force ambient air through theheat exchanger, and a thermostat 51 which operates the fan when fluidcontained within cooler 52 exceed a predetermined temperature.

Proportional control valve assembly 40 is disposed serially with respectto the supply conduit and is interposed between the outlet of pump 36and the inlet of motor 38. Control valve assembly 40 is controlled by anautomatic control circuit shown in FIG. 4 which will be describedhereinafter. As seen in FIG. 3, valve assembly 40 includes a housing 58enclosing a valve chamber 60, a first fluid passage 62 and a secondfluid passage 64, wherein fluid passages 62, 64 are disposed in fluidcommunication with chamber 60. Passage 62 is disposed serially withrespect to supply conduit sections 44A, 44B. Passage 64 is connected influid communication with the return conduit comprising sections 46A,46E. A bleed conduit 66 discharges a minor quantity of fluid from motor38 directly to tank 54. A drain line 68 is provided for draining fluidfrom the hydraulic circuit for maintenance and repairs.

Valve assembly 40 is seen to be a closed center electrohydraulic servocontrol valve assembly incorporating a spool valve which shuttlesreciprocatingly within housing 58 such that flow in passages 62 and 64can proceed in a first direction, in an opposite direction, or isentirely obstructed when the spool valve is in the center position. Thevalve is so configured that flow rate in both directions isprogressively metered or varied. Solenoids 70, 72 move the spool valveresponsively to signals generated by the automatic control circuit shownin FIG. 4. It is an important feature of the invention that passages 62and 64 are dimensioned and configured such that each passage 62 or 64 isof the minimum cross sectional surface area occurring within theirrespective supply conduit sections 46A . . . 46E and return conduitsections 44A, 44B.

Apart from hydraulic pump 36 and fluid conduits connected to pump 36,most of the hydraulic components are mounted within a housing 74. Thisenables the hydraulic components to be readily installed as a unitwithin vehicle 10. As best seen in FIG. 1, installation of the hydrauliccomponents requires only that pump 36 be connected to power take-off 32,housing 74 be suitably mounted to chassis 12, and fluid connections bemade between pump 36 and components contained within housing 74.

The control circuit is shown in FIG. 4. The control circuit controlsvalve assembly 40 such that valve assembly 40 selectively controls fluidflow within passages 62, 64 by generating signals which operatesolenoids 70, 72. Signals are generated by the following method. A tab75 is affixed to shaft 42 of hydraulic motor 38. A sensor 76 sensesrotational speed of motor 38 and shaft 42 by detecting passage of tab 75past sensor 76 at each revolution of shaft 42, and responsively sends asignal to a microprocessor or data processor or central processing unit78. Sensor 76 is preferably an eddy current sensor mounted in a fixedposition proximate shaft 42. A preferred arrangement is shown in moredetail in U.S. Pat. No. 5,908,183, which patent is hereby incorporatedby reference.

Central processing unit 78 is operably connected to a reference signalgenerator disposed to generate a reference signal indicative of adesired predetermined rate of rotation of generator 34. The referencesignal generator is preferably digital variable pulse generator 80. Analgebraic comparing subcircuit 82 is disposed to compare sensedrotational speed of hydraulic motor 38 with the reference signal.Comparing subcircuit 82 generates a control signal controlling solenoids70, 72, and hence the spool valve of control valve assembly 40 in amanner assuring that rate of fluid conducted to supply conduit sections44A, 44B be constant independently of any changes in the rate of fluiddischarged by hydraulic pump 36.

Certain annunciation and control elements of the control circuit areprovided in a location on vehicle 10 enabling ready access to operatingpersonnel. These elements include a digital display 84 operablyconnected to the control circuit. Digital display 84 displays real timevalues of generator output voltage, generator output frequency,generator output amperage, generator rotational speed, and elapsed timeof generator operation. Central processing unit 78 serves in part as avoltage regulator disposed to adjust voltage output of generator 34 to apredetermined voltage. If a voltage value displayed on digital display84 is not satisfactory, then adjustments may be entered by a keypad 8Goperably associated with a non-volatile memory 88 and operably connectedto central processing unit 78. A remote “on-off” or “start-stop” switch90 is also operably connected to central processing unit 78 to operateand cease operation of generator 34.

Another feature of the control circuit is a “soft start” or rampingsubcircuit 92, which modifies the control signal to solenoids 70, 72such that when started from a stopped condition, generator 34accelerates gradually and smoothly up to the selected rotational speed.The period of time of acceleration to full operating speed is preferablyadjustable within a range of ten seconds to one minute. The period foracceleration can be adjusted by commands entered by keypad 86. Gradualacceleration of generator 34 is a protective feature which eliminatessevere stresses which would otherwise be imposed on the hydrauliccircuit in the event of unduly abrupt or harsh acceleration.

Another protective feature is that of a circuit breaker 94 which islocated in series with output conductors 96 connected to the outputterminals (not separately shown) of generator 34. Output conductors willbe understood to include all necessary conductors, such as neutral andground as well as live phase conductors. Circuit breaker 94 operatesconventionally by opening an external circuit (not shown) which isconnected to conductors 96 to conduct electrical power to poweredequipment.

The present invention is susceptible to variations and modificationswhich may be introduced thereto without departing from the inventiveconcept. For example, the valve four-way valve assembly depicted hereincould alternatively be a single throttled proportional valve. Additionalexamples include but are not limited to the following. Control of theproportional valve may utilize generator output frequency as an input.Where generator capacity is relatively great, such as seven and one halfkilowatts and greater, both frequency and shaft speed sensing are usedto control a four way proportional valve. The shaft speed control signalis connected to one side of the coil of the solenoid valve, and a signalderived from the generator output frequency is connected to the otherside of the coil. This procedure is preferred to properly controlrelatively great volumes and pressures of hydraulic fluid. Control of asingle or four-way valve can use frequency sensing or shaft speedsensing, or a combination of both, depending upon the application.

The power train components (i.e., engine 14, transmission 16, driveshaft26, differential gear assembly 28, and rear axle 30) may be arrangeddifferently from the depiction of FIG. 1. Illustratively, the engine maybe located at any one of diverse locations with respect to chassis 12. Atransaxle (not shown) may be utilized if desired. More or fewer than twowheels may be powered. A hydraulic power transmission scheme may besubstituted for the mechanical transmission components described herein.The motor vehicle may be a boat driven by a propeller or by a water pumparrangement, or an aircraft. It is merely necessary for the purposes ofthe present invention that the associated motor vehicle have an engineand be self-propelled.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the following claims.

I claim:
 1. Apparatus for driving a generator carried aboard a motorvehicle having an engine and a power take-off at a constant speeddespite fluctuations in rotational speed of the engine, comprising: ahydraulic pump connectable to the power take-off to be driven thereby,having an inlet disposed to receive fluid for pumping and an outlet fordischarging pumped fluid under pressure; a hydraulic motor drivablyconnectable to the generator, having an inlet disposed to receive fluidunder pressure and an outlet disposed to discharge spent fluid; a fluidcircuit comprising a supply conduit disposed to conduct fluid dischargedby said pump to said motor, a return conduit disposed to return fluiddischarged by said motor to said pump, and a recirculating conduitdisposed to return fluid discharged by said pump to said inlet of saidpump; a proportional control valve assembly disposed serially withrespect to said supply conduit and interposed between said outlet ofsaid pump and said inlet of said motor, said control valve assemblyhaving a housing having a valve chamber, a valve disposed within saidvalve chamber, a solenoid disposed to move said valve within said valvechamber, a first fluid passage disposed in fluid communication with saidvalve chamber, a second fluid passage disposed in communication withsaid valve chamber, wherein said valve selectively closes and opens saidfirst fluid passage and said second fluid passage, wherein said firstfluid passage of said valve assembly is disposed within said supplyconduit and said second fluid passage of said valve assembly isconnected in fluid communication with said return conduit, and whereinsaid first fluid passage is dimensioned and configured such that saidfirst fluid passage is of the minimum cross sectional surface areaoccurring within said supply conduit, and said second fluid passage isdimensioned and configured such that said second fluid passage isdimensioned and configured such that said second fluid passage is of theminimum cross sectional surface area occurring within said returnconduit; and a control circuit disposed to control said valve assemblysuch that said valve assembly controls fluid flow within said firstfluid outlet of said valve assembly and said second fluid outlet of saidvalve assembly, wherein said control circuit includes a sensor disposedto sense rotational speed of said motor, a reference signal generatordisposed to generate a reference signal indicative of a predeterminedrate of rotation, and a comparing subcircuit disposed to compare sensedrotational speed of said motor with said reference signal, and togenerate a control signal controlling said valve assembly in a mannerassuring that rate of fluid conducted to said supply conduit be constantindependently of rate of fluid discharged by said pump.
 2. The apparatusaccording to claim 1, wherein said control valve assembly is anelectrohydraulic servo control valve assembly.
 3. The apparatusaccording to claim 1, wherein said reference signal generator is adigital variable pulse generator.
 4. The apparatus according to claim 1,further including a digital display connected to said control circuit,wherein said digital display is disposed to display real time values ofgenerator output voltage, generator output frequency, generator outputamperage, generator rotational speed, and elapsed time of generatoroperation.
 5. The apparatus according to claim 1, wherein said fluidcircuit includes a fluid storage tank disposed serially with respect tosaid return conduit.
 6. The apparatus according to claim 5, wherein saidfluid circuit further includes a hydraulic fluid filter disposedserially with respect to said return conduit.
 7. The apparatus accordingto claim 5, wherein said fluid circuit further includes a hydraulicfluid cooler disposed serially with respect to said return conduit, anelectrically operated fan disposed to pass ambient air through saidhydraulic fluid cooler, and a thermostat disposed to operate said fanwhen fluid contained within said hydraulic fluid cooler attainstemperatures exceeding a predetermined temperature.
 8. The apparatusaccording to claim 7, wherein said fluid circuit further includes ahydraulic fluid filter disposed serially with respect to said returnconduit, and a housing enclosing said hydraulic motor, said controlvalve assembly, said fluid filter, said fluid cooler, and said fluidstorage tank, whereby said hydraulic motor, said control valve assembly,said fluid filter, said fluid cooler, and said fluid storage tank arereadily installed as a unit on the chassis of the motor vehicle.
 9. Theapparatus according to claim 1, wherein said generator has outputconductors and a circuit breaker disposed to open a circuit connected tosaid output conductors.
 10. The apparatus according to claim 1, furthercomprising a voltage regulator disposed to adjust voltage output of saidgenerator to a predetermined voltage.
 11. The apparatus according toclaim 1, wherein said hydraulic motor has a rotatable shaft, and saidsensor includes a projection ixed to said rotatable shaft of saidhydraulic motor and an eddy current sensor mounted in a fixed positionrelative to and proximate said projection and said rotatable shaft. 12.The apparatus according to claim 1, wherein said sensor is responsive togenerator output frequency.
 13. The apparatus according to claim 1,wherein said control circuit has a ramping subcircuit disposed to modifysaid control signal of said comparing subcircuit controlling saidcontrol valve assembly such that acceleration of said generator isaccomplished in a time period of at least ten seconds.
 14. The apparatusaccording to claim 13, wherein said ramping subcircuit is adjustablesuch that the time period of acceleration of said generator isadjustable within a range of ten seconds to one minute.
 15. Apparatusfor driving a generator carried aboard a motor vehicle having an engineand a power take-off at a constant speed despite fluctuations inrotational speed of the engine, comprising: a hydraulic pump connectableto the power take-off to be driven thereby, having an inlet disposed toreceive fluid for pumping and an outlet for discharging pumped fluidunder pressure, a hydraulic motor drivably connectable to the generator,having an inlet disposed to receive fluid under pressure and an outletdisposed to discharge spent fluid; a fluid circuit comprising a supplyconduit disposed to conduct fluid discharged by said pump to said motor,a return conduit disposed to return fluid discharged by said motor tosaid pump, a recirculating conduit disposed to return fluid dischargedby said pump to said inlet of said pump, a fluid storage tank disposedserially with respect to said return conduit, a hydraulic fluid filterdisposed serially with respect to said return conduit, a hydraulic fluidcooler disposed serially with respect to said return conduit, anelectrically operated fan disposed to pass ambient air through saidhydraulic fluid cooler, and a thermostat disposed to operate said fanwhen fluid contained within said hydraulic fluid cooler attainstemperatures exceeding a predetermined temperature, and a hydraulicfluid filter disposed serially with respect to said return conduit, anda housing enclosing said hydraulic motor, said control valve assembly,said fluid filter, said fluid cooler, and said fluid storage tank,whereby said hydraulic motor, said control valve assembly, said fluidfilter, said fluid cooler, and said fluid storage tank are readilyinstalled as a unit on the chassis of the motor vehicle; anelectrohydraulic, closed center, proportional servo control valveassembly disposed serially with respect to said supply conduit andinterposed between said outlet of said pump and said inlet of saidmotor, said control valve assembly having a housing having a valvechamber, a valve disposed within said valve chamber, a solenoid disposedto move said valve within said valve chamber, a first fluid passagedisposed in fluid communication with said valve chamber, a second fluidpassage disposed in communication with said valve chamber, wherein saidvalve selectively closes and opens said first fluid passage and saidsecond fluid passage, wherein said first fluid passage of said valveassembly is disposed within said supply conduit and said second fluidpassage of said valve assembly is connected in fluid communication withsaid return conduit, and wherein said first fluid passage is dimensionedand configured such that said first fluid passage is of the minimumcross sectional surface area occurring within said supply conduit, andsaid second fluid passage is dimensioned and configured such that saidsecond fluid passage is dimensioned and configured such that said secondfluid passage is of the minimum cross sectional surface area occurringwithin said return conduit; and a control circuit disposed to controlsaid valve assembly such that said valve assembly controls fluid flowwithin said first fluid outlet of said valve assembly and said secondfluid outlet of said valve assembly, wherein said control circuitincludes a sensor disposed to sense rotational speed of said motor,wherein said hydraulic motor has a rotatable shaft, and said sensorincludes a projection fixed to said rotatable shaft of said hydraulicmotor and an eddy current sensor mounted in a fixed position proximatesaid rotatable shaft and said projection, a reference signal generatordisposed to generate a reference signal indicative of a predeterminedrate of rotation, wherein said reference signal generator is a digitalvariable pulse generator, a comparing subcircuit disposed to comparesensed rotational speed of said motor with said reference signal, and togenerate a control signal controlling said valve assembly in a mannerassuring that rate of fluid conducted to said supply conduit be constantindependently of rate of fluid discharged by said pump, a digitaldisplay connected to said control circuit, wherein said digital displayis disposed to display real time values of generator output voltage,generator output frequency, generator output amperage, generatorrotational speed, and elapsed time of generator operation, a rampingsubcircuit disposed to modify said control signal of said comparingsubcircuit controlling said control valve assembly such thatacceleration of said generator is accomplished in a time periodadjustable within a range of ten seconds to one minute, and a voltageregulator disposed to adjust voltage output of said generator to apredetermined voltage, wherein said generator has output conductors anda circuit breaker disposed to open a circuit connected to said outputconductors.
 16. Apparatus for driving a generator carried aboard a motorvehicle having an engine and a power take-off at a constant speeddespite fluctuations in rotational speed of the engine, comprising: ahydraulic pump connectable to the power take-off to be driven thereby,having an inlet disposed to receive fluid for pumping and an outlet fordischarging pumped fluid under pressure; a hydraulic motor drivablyconnectable to the generator, having an inlet disposed to receive fluidunder pressure and an outlet disposed to discharge spent fluid; a fluidcircuit comprising a supply conduit disposed to conduct fluid dischargedby said pump to said motor, a return conduit disposed to return fluiddischarged by said motor to said pump, a recirculating conduit disposedto return fluid discharged by said pump to said inlet of said pump, afluid storage tank disposed serially with respect to said returnconduit, a hydraulic fluid filter disposed serially with respect to saidreturn conduit, a hydraulic fluid cooler disposed serially with respectto said return conduit, an electrically operated fan disposed to passambient air through said hydraulic fluid cooler, and a thermostatdisposed to operate said fan when fluid contained within said hydraulicfluid cooler attains temperatures exceeding a predetermined temperature,and a hydraulic fluid filter disposed serially with respect to saidreturn conduit, and a housing enclosing said hydraulic motor, saidcontrol valve assembly, said fluid filter, said fluid cooler, and saidfluid storage tank, whereby said hydraulic motor, said control valveassembly, said fluid filter, said fluid cooler, and said fluid storagetank are readily installed as a unit on the chassis of the motorvehicle; an electrohydraulic, closed center, proportional servo controlvalve assembly disposed serially with respect to said supply conduit andinterposed between said outlet of said pump and said inlet of saidmotor, said control valve assembly having a housing having a valvechamber, a valve disposed within said valve chamber, a solenoid disposedto move said valve within said valve chamber, a first fluid passagedisposed in fluid communication with said valve chamber, a second fluidpassage disposed in communication with said valve chamber, wherein saidvalve selectively closes and opens said first fluid passage and saidsecond fluid passage, wherein said first fluid passage of said valveassembly is disposed within said supply conduit and said second fluidpassage of said valve assembly is connected in fluid communication withsaid return conduit, and wherein said first fluid passage is dimensionedand configured such that said first fluid passage is of the minimumcross sectional surface area occurring within said supply conduit, andsaid second fluid passage is dimensioned and configured such that saidsecond fluid passage is dimensioned and configured such that said secondfluid passage is of the minimum cross sectional surface area occurringwithin said return conduit; and a control circuit disposed to controlsaid valve assembly such that said valve assembly controls fluid flowwithin said first fluid outlet of said valve assembly and said secondfluid outlet of said valve assembly, wherein said control circuitincludes a sensor disposed to sense generator output frequency, areference signal generator disposed to generate a reference signalindicative of a predetermined rate of rotation, wherein said referencesignal generator is a digital variable pulse generator, a comparingsubcircuit disposed to compare sensed output frequency of said generatorwith said reference signal, and to generate a control signal controllingsaid valve assembly in a manner assuring that rate of fluid conducted tosaid supply conduit be constant independently of rate of fluiddischarged by said pump, a digital display connected to said controlcircuit, wherein said digital display is disposed to display real timevalues of generator output voltage, generator output frequency,generator output amperage, generator rotational speed, and elapsed timeof generator operation, a ramping subcircuit disposed to modify saidcontrol signal of said comparing subcircuit controlling said controlvalve assembly such that acceleration of said generator is accomplishedin a time period adjustable within a range of ten seconds to one minute,and a voltage regulator disposed to adjust voltage output of saidgenerator to a predetermined voltage, wherein said generator has outputconductors and a circuit breaker disposed to open a circuit connected tosaid output conductors.
 17. A motor vehicle having an engine and anonboard AC generator driven by said engine, wherein said AC generator iscontrolled to operate at a selected constat rotational speedindependently of fluctuations in rotational speeds of said engine,comprising: a chassis and a plurality of road wheels suspended from saidchassis, a power train drivably connected to said road wheels, whereinsaid power train includes an engine, a transmission having a rotatableshaft driven by said engine, and a power take-off driven by saidrotatable shaft of said transmission; a generator supported on saidchassis; and apparatus for driving said generator, comprising ahydraulic pump connectable to the power take-off to be driven thereby,having an inlet disposed to receive fluid for pumping and an outlet fordischarging pumped fluid under pressure; a hydraulic motor drivablyconnectable to the generator, having an inlet disposed to receive fluidunder pressure and an outlet disposed to discharge spent fluid; a fluidcircuit comprising a supply conduit disposed to conduct fluid dischargedby said pump to said motor, a return conduit disposed to return fluiddischarged by said motor to said pump, a recirculating conduit disposedto return fluid discharged by said pump to said inlet of said pump, afluid storage tank disposed serially with respect to said returnconduit, a hydraulic fluid filter disposed serially with respect to saidreturn conduit, a hydraulic fluid cooler disposed serially with respectto said return conduit, an electrically operated fan disposed to passambient air through said hydraulic fluid cooler, and a thermostatdisposed to operate said fan when fluid contained within said hydraulicfluid cooler attains temperatures exceeding a predetermined temperature,and a hydraulic fluid filter disposed serially with respect to saidreturn conduit, and a housing enclosing said hydraulic motor, saidcontrol valve assembly, said fluid filter, said fluid cooler, and saidfluid storage tank, whereby said hydraulic motor, said control valveassembly, said fluid filter, said fluid cooler, and said fluid storagetank are readily installed as a unit on the chassis of the motorvehicle; an electrohydraulic, closed center, proportional servo controlvalve assembly disposed serially with respect to said supply conduit andinterposed between said outlet of said pump and said inlet of saidmotor, said control valve assembly having a housing having a valvechamber, a valve disposed within said valve chamber, a solenoid disposedto move said valve within said valve chamber, a first fluid passagedisposed in fluid communication with said valve chamber, a second fluidpassage disposed in communication with said valve chamber, wherein saidvalve selectively closes and opens said first fluid passage and saidsecond fluid passage, wherein said first fluid passage of said valveassembly is disposed within said supply conduit and said second fluidpassage of said valve assembly is connected in fluid communication withsaid return conduit, and wherein said first fluid passage is dimensionedand configured such that said first fluid passage is of the minimumcross sectional surface area occurring within said supply conduit, andsaid second fluid passage is dimensioned and configured such that saidsecond fluid passage is dimensioned and configured such that said secondfluid passage is of the minimum cross sectional surface area occurringwithin said return conduit; and a control circuit disposed to controlsaid valve assembly such that said valve assembly controls fluid flowwithin said first fluid passage of said valve assembly and said secondfluid passage of said valve assembly, wherein said control circuitincludes a sensor disposed to sense rotational speed of said motor,wherein said hydraulic pump has a rotatable shaft, and said sensorincludes a projection fixed to said rotatable shaft of said hydraulicpump and an eddy current sensor mounted in a fixed position proximatesaid rotatable shaft and said projection, a reference signal generatordisposed to generate a reference signal indicative of a predeterminedrate of rotation, wherein said reference signal generator is a digitalvariable pulse generator, a comparing subcircuit disposed to comparesensed rotational speed of said motor with said reference signal, and togenerate a control signal controlling said valve assembly in a mannerassuring that rate of fluid conducted to said supply conduit be constantindependently of rate of fluid discharged by said pump, a digitaldisplay connected to said control circuit, wherein said digital displayis disposed to display real time values of generator output voltage,generator output, frequency, generator output amperage, generatorrotational speed, and elapsed time of generator operation, a rampingsubcircuit disposed to modify said control signal of said comparingsubcircuit controlling said control valve assembly such thatacceleration of said generator is accomplished in a time periodadjustable within a range of ten seconds to one minute, and a voltageregulator disposed to adjust voltage output of said generator to apredetermined voltage, and wherein said generator has output conductorsand a circuit breaker disposed to open a circuit connected to saidoutput conductors.
 18. A motor vehicle having an engine and an onboardAC generator driven by said engine, wherein said AC generator iscontrolled to operate at a selected constat rotational speedindependently of fluctuations in rotational speeds of said engine,comprising: a chassis and a plurality of road wheels suspended from saidchassis, a power train drivably connected to said road wheels, whereinsaid power train includes an engine, a transmission having a rotatableshaft driven by said engine, and a power take-off driven by saidrotatable shaft of said transmission; a generator supported on saidchassis; and apparatus for driving said generator, comprising ahydraulic pump connectable to the power take-off to be driven thereby,having an inlet disposed to receive fluid for pumping and an outlet fordischarging pumped fluid under pressure; a hydraulic motor drivablyconnectable to the generator, having an inlet disposed to receive fluidunder pressure and an outlet disposed to discharge spent fluid; a fluidcircuit comprising a supply conduit disposed to conduct fluid dischargedby said pump to said motor, a return conduit disposed to return fluiddischarged by said motor to said pump, a recirculating conduit disposedto return fluid discharged by said pump to said inlet of said pump, afluid storage tank disposed serially with respect to said returnconduit, a hydraulic fluid filter disposed serially with respect to saidreturn conduit, a hydraulic fluid cooler disposed serially with respectto said return conduit, an electrically operated fan disposed to passambient air through said hydraulic fluid cooler, and a thermostatdisposed to operate said fan when fluid contained within said hydraulicfluid cooler attains temperatures exceeding a predetermined temperature,and a hydraulic fluid filter disposed serially with respect to saidreturn conduit, and a housing enclosing said hydraulic motor, saidcontrol valve assembly, said fluid filter, said fluid cooler, and saidfluid storage tank, whereby said hydraulic motor, said control valveassembly, said fluid filter, said fluid cooler, and said fluid storagetank are readily installed as a unit on the chassis of the motorvehicle; an electrohydraulic, closed center, proportional servo controlvalve assembly disposed serially with respect to said supply conduit andinterposed between said outlet of said pump and said inlet of saidmotor, said control valve assembly having a housing having a valvechamber, a valve disposed within said valve chamber, a solenoid disposedto move said valve within said valve chamber, a first fluid passagedisposed in fluid communication with said valve chamber, a second fluidpassage disposed in communication with said valve chamber, wherein saidvalve selectively closes and opens said first fluid passage and saidsecond fluid passage, wherein said first fluid passage of said valveassembly is disposed within said supply conduit and said second fluidpassage of said valve assembly is connected in fluid communication withsaid return conduit, and wherein said first fluid passage is dimensionedand configured such that said first fluid passage is of the minimumcross sectional surface area occurring within said supply conduit, andsaid second fluid passage is dimensioned and configured such that saidsecond fluid passage is dimensioned and configured such that said secondfluid passage is of the minimum cross sectional surface area occurringwithin said return conduit; and a control circuit disposed to controlsaid valve assembly such that said valve assembly controls fluid flowwithin said first fluid passage of said valve assembly and said secondfluid passage of said valve assembly, wherein said control circuitincludes a sensor disposed to sense output frequency of said generator,a reference signal generator disposed to generate a reference signalindicative of a predetermined rate of rotation, wherein said referencesignal generator is a digital variable pulse generator, a comparingsubcircuit disposed to compare sensed output frequency of said generatorwith said reference signal, and to generate a control signal controllingsaid valve assembly in a manner assuring that rate of fluid conducted tosaid supply conduit be constant independently of rate of fluiddischarged by said pump, a digital display connected to said controlcircuit, wherein said digital display is disposed to display real timevalues of generator output voltage, generator output frequency,generator output amperage, generator rotational speed, and elapsed timeof generator operation, a ramping subcircuit disposed to modify saidcontrol signal of said comparing subcircuit controlling said controlvalve assembly such that acceleration of said generator is accomplishedin a time period adjustable within a range of ten seconds to one minute,and a voltage regulator disposed to adjust voltage output of saidgenerator to a predetermined voltage, and wherein said generator hasoutput conductors and a circuit breaker disposed to open a circuitconnected to said output conductors.